Electric arc furnaces for melting metal especially steel generally have three vertical electrodes arranged in a triangle and held by horizental parallel support arms and are operated as three-phase furnaces. Only for special purposes, for example in the pre-melting of slag in the slag reaction method are they provided with one electrode and operated as single-phase furnaces.
Furnaces of this type for a long time have suffered from the well known problem that the electrodes break off from the support arm at the point where they are clamped in. In a furnace equipped with three electrodes the breakage rate amounted to five to ten per month. After changing over to higher melt output rates (heavier current,) the breakage rate increased to 30 to 40 per month. The central electrode was particularly vulnerable, i.e. when the electrodes were arranged in a triangle and when the electrodes were held by parallel support arms and the electrode was fixed to the shorter central support arm.
A possible solution for reducing the breakage rate by stiffening the support construction becomes problematic because of the increase in the mass associated therewith, since bigger masses also require a stronger drive for lifting and lowering the support arm construction. A reduction in the breakage rate by improving the mechanical properties of the electrodes therefore results in an increase in cost.
Another proposal for reducing the breakage rate of the electrodes consists in a damping device positioned on the support arm of the respective electrode. The damping device includes a neutral mass, which is coupled to the support arm by a spring and which can move normally in respect to the common plane of the electrode and the support arm under the oscillations of the arm. The movement of the mass is damped by damping means, for instance by a hydraulic fluid in which the mass is embedded. The basic idea of this solution is to absorb the oscillations in the damping material where the mechanical energy is converted into heat. It has been found that this method is not effective in protecting the electrodes against breakage as disclosed in unexamined German patent application No. 2837741.
It is the object of the invention to provide an electric arc furnace in which the danger of breakage of the electrodes is reduced in comparison with those of conventional arc furnaces.